Information on the modulation and synaptic regulation of neuronal nicotinic acetylcholine receptors (AChRs) is at a primitive stage. Of particular interest is the modulation of neuronal AChRs by neural peptides, such as substance P. Since peptide co-existence with classical neurotransmitters is common to both central and peripheral neurons, the mechanism of receptor modulation by peptides is of general importance. In addition to the short term modulation of neuronal ACh responses, the properties and distribution of AChRs may be regulated by synaptogenesis. We will also examine the influence of presynaptic input in the regulation of transmitter sensitivity and neuronal AChR channels. Our first aim is to characterize the ACh sensitivity as well as the conductance and kinetics of individual AchRs of embryonic lumbar sympathetic neurons removed just prior to synaptogenesis. These studies use macroscopic ACh-evoked current as well as single channel recording and provide a framework for proposed studies of AChR modulation by peptides and their regulation following synapse formation. We will pursue our initial studies of the role of phosphorylation in peptide modulation of neuronal AChRs by combining physiological and biochemical approaches. We will measure ACh-elicited currents in cells and membrane patches following activation or inhibition of specific kinases. These data will be compared with peptide effects on second messenger metabolism. Finally, we will examine the potential physiological role of modulation and the regulation of AChR properties in innervated sympathetic neurons. In sum, the proposed studies should better define the physiology and biochemical mechanism of AChR modulation as well as the synaptic regulation of this receptor critical to signal transduction at central as well as peripheral synapses.